Our work has focused primarily on the membrane components which control red cell shape and deformability. From a physiological and pathological point of view, deformability is one of the most important RBC membrane properties. Alterations in membrane deformability are important in the pathogenesis of many hemolytic anemias, in the storage $ and transfusion of blood, and probably in the release of reticulocytes into the circulation and the removal of senile RBCs at the end of their circulatory life-span. We have been particularly interested in the role of spectrin in the control of membrane shape and deformability. Our recent work has provided direct evidence that spectrin makes a major contribution to these properties.